As biaxially oriented polyester films, a biaxially oriented laminated polyester film is known (for instance, U.S. Pat. Nos. 5,069,962 and 5,626,942). There is also known a biaxially oriented polypropylene terephthalate film (Japanese Unexamined Patent Publication No. 9-175055 for example).
Such a commonly known, biaxially oriented polyester film when in use for magnetic recording media affords improved electromagnetic conversion characteristics, but leaves the problem that polymer particles become escaped due to insufficient wear resistance of the polymer surface, eventually inviting particle dusting. Upon application to magnetic tapes, this type of polyester film involves the lack of signals which would result from particle dusting. In magnetic recording media of a higher density, a need exists for those physical characteristics that could prevent polymer particles from escaping out of the corresponding polyester film. In order to solve these problems, a principal object of the present invention is to provide a biaxially oriented polyester film which, in particular, is excellent in wear resistance and free from oligomer separation.